Upright piano action



y 20, 1958 w. w. WATERS 2,835,157

UPRIGHT PIANO ACTION Filed April 18, 1956 2 Sheets-Sheet 1 INVENTOR.

W/LBUR w. WATERS,

. ATTORNEY.

y 20, 1958 w. w. WATERS 2,835,157

UPRIGHT PIANO AcTioN Filed April 18. 195a 2 Sheets-Sheet 2 INVEN TOR I W/LBUR W. WATERS [BY WW ATTORNEY.

United States Patent Office 2,835,157 Patented May 20, 1958 UPRIGHT PIANO ACTION Wilbur W. Waters, Kirkville, N. Y.

Application April 18, 1956, Serial No. 579,074

7 Claims. (Cl. 84-440) The present invention relates to piano actions and has as a particular object thereof the provision of an improved piano action particularly adapted for use in piano instruments whose strings lie in a vertical plane.

The piano action is the intermediate mechanical linkage. transferring motion of the keys and pedals to the hammers and dampers. The term piano action is commonly used to denote both the collective 88 like mechanisms for the entire keyboard as well as one individual mechanism associated with one key and the strings responding to that key. The term will be subsequently employed in both senses.

In the field of piano instruments, the grand piano, in which the strings lie in a horizontal plane, has long been preferred over the standard upright and spinet pianos in which the strings lie in a vertical plane. One principal reason for this preference has been the inadequacy of conventional upright piano actions particularly in respect to positiveness of repetition and rapidity of repetition when compared to the actions in grand pianos.

The difference in effecting hammer return between grand and upright pianos is the underlying cause for this difference in repetition. In the grand piano, the hammer, whose principal mass travels in an approximately vertical arcuate path from the hammer rail to the string, has nearly the full benefit of gravitational force in returning the hammer from the string to rest position. In the case of grand pianos, the force of gravity acting on the mass of the hammer is the only force required for hammer retraction and it proves to be a highly satisfactory motive force.

In the upright piano, the principal mass of the hammer travels in a nearly horizontal arcuate path from the hammer rail to the string, and the force of gravity can only act upon this mass with a small fraction of its effective force along this path. In most vertical pianos, as the hammer traverses the return path from the string to the rail, this reduced gravitational force upon the hammer first urges the hammer toward the string when the hammer is in close proximity to the string thus impeding its return, then goes through a null point after which it aids return of the hammer to the hammer rail.

Since the gravitational force component elfective for hammer return in upright actions is small and changing in direction, it cannot be relied on for hammer return in such actions. Accordingly, some additional mechanism either powered by gravity or by a spring is usually employed. The most common mechanism in use at the present time is the bridle strap, a small piece of flexible material attached between the butt of the hammer and an intermediate member of appreciable weight, often denoted the wippen. The wippen is adapted to fall relatively rapidly under the influence of gravity, drawing the hammer back with it by means of the bridle strap. On occasion, springs have been used as the sole motive force for hammer return, but in such strenuous service a tendency to lose resilience and to excite unwanted vibrations in the hammer motion has discouraged a more general use.v

2 Springs, however, have been combined with gravity-op erated bridle-strap systems. As will no doubt be appreciated, combining these measures leads to piano actions which are complicated in structure and difficult to assemble and yet not so satisfactory in operation as grand piano actions.

It is an object of the present invention to provide an improved piano action foran upright piano which is simple in structure and readily adapted to assembly.

It is another object of the present invention to provide an improved piano action for upright pianos which is capable of rapid and positive repetition.

It is a further object of the present invention to provide an improved piano action which is readily regulated and easily disassembled.

These and other objects are achieved in accordance with the present invention in a novel action for upright pianos wherein the hammer is engaged with the wippen for acceleration of the return of the hammer to the rail by means of a resilient member adapted to provide an initial loose resilient engagement urging the hammer backwards followed by a more positive engagement which greatly accelerates the hammer toward rest position. In accordance with one embodiment of the invention, a helical spring having two axially extending ends, one end secured to the hammer butt, and the other end having a hook adapted to engage the back check which is mounted on the wippen, provides for rapid return of the hammer after a blow is struck upon the strings.

In accordance with a second embodiment of the invention, an elongated spring of circular or flattened rectangular cross section is employed having the one end secured to the hammer butt, the other end having a hook adapted to engage the back check, and having the intermediate portion bent so as to always exert a hammer return force upon the hammer butt.

In accordance with another aspect of the invention,

the jack and back check are arranged between the main action rail and the regulating button rail, a feature which permits easy access to the regulating button for regulation, holds the lower part of the action in place when the piano keys and other parts of the action are removed, and by reducing the distance between the hammer and back check permits simplified integration of the usual hammer butt heel into the hammer butt.

In accordance with a further aspect of the invention, applicants novel hammer spring removably engaged with the back check, which eliminates the need for the customary hammer spring rail mounted above the main action rail, in cooperation with the integral assembly of the hammer and damper flanges, provides rapid assembly or removal of the damper and hammer as a unit from the action rail.

Inaccordance with still another aspect of the invention, the jack is provided with a deformable spoon, adapted to directly contact the under surface of the regulating rail in the operation of the action, deformation of the spoon providing a simplified method of regulating the action which eliminates the need for the more costly screw threaded regulating button mounted upon the regulating rail.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. For a more thorough understanding of the invention, however, together with other aspects thereof, advantages pertaining thereto, and further objects thereof, reference may now be made to the following description taken in connection with the accompanying drawings, in which;

Figure 1 is a view of a piano action built in accordance with the present invention, the mechanism being illustrated in rest position;

Figure 2 is a second view of the embodiment illustrated in Figure l, the mechanism being illustrated with the hammer in checked position;

Figure v3 is a third view of the embodiment illustrated in .Figure .1, the mechanism being illustrated just subse quent to checking as the hammer is returning to the hammer rail;

Figure 4 illustrates a further embodiment of the invention wherein the hammer spring and regulating rail are modified.

Referring .now to Figures 1, 2 and 3, a piano action built in accordancewith the present invention is shown. The .hammer ofthe piano action is arranged to strike the vertically oriented string 11, a portion of which is shown in the drawings, when actuated by the piano key 12, also only partially shown. The damper 13 is likewise actuated by the key 12. The principal parts comprising the piano action are supported in position with respect tothe string .11 and the piano key 12 upon the main action rail 14.

The hammer 10 is constructed of three principal wooden parts: the hammer moulding 15, the hammer shank 16, and the hammer butt 17. The hammer moulding 15 has an elongated tapered portion upon which the inner hammer felt 18 and the outer hammer felt 19 are secured. The hammer felt 19 is the portion of the hammer which strikes the string 11. At the other end of the hammer moulding 15, a cylindrical socket, whose axis is generally perpendicular tothe axis of the hammer moulding, is provided for reception of one end of the hammer shank 16'. The hammer butt 17 is also provided with a cylindrical socket 20 into which the other end of the hammer shank 16 is fitted. As will appear in the subsequent discussion, certain as yet unspecified features of construction of the hammer butt 17 are of particular interest.

The hammer '10 is supported by and pivots as a unit about the lower portion 21 of the hammer butt 17 which portion is fitted into a slot formed in the bifurcated end of the joint hammer-damper flange 22. The hammer-damper flange 22 is secured in a position inclined tothe horizontal uponthe upper'surface of the main'action rail 14 by means of a screw 23.

The damper 13.has four principal structural parts including the elongated wooden damper rod 24, the wooden damper block 25, the wooden damper moulding 26, and the damper wire'27. The damper rod 24 supports the damper block 25, and damper moulding 26 secured to the damper block by means of the damper wire 27 which is secured in the upper end of the damper rod 24. A set screw 28 in the damper block 25, through which the damper wire passes, permits vertical adjustment of the position of damper block with respect to the string 11. The damper felt 29 pads the front face of the damper moulding 26 where string contact is made.

The damper is pivotally supported as a unit upon the upper bifurcated portion 3!} of the hammer-damper flange 22. The damper 13 is supported at a bearing 31 of reduced thickness to permit entry into the bifurcated portion 30, fashioned at an intermediate point along the axis of the damper rod 24. The damper 13 is further provided with a spring 32.normally urging the damper into engagement with the piano string 11. The spring 32 is supported upon the hammer-damper flange 22 and has its upper surfaceengaginga padded recess in the upper portion of the damper rod 24.

The description of'the invention has so far concerned itself with a brief discussion of the construction of the hammer 1t) and damper 13 and their mode of support upon the main action rail 14. The hammer 10 produces tones upon striking the strings to cause vibration thereof, and the damper .13 which normally presses against the strings to prevent vibration thereof is at the same time rotated away from the strings.

The joint control of the hammer 10 and the damper 13 is the function of the portions of the piano action now to be described.

Simultaneous impulsion of the hammer 10 and retraction of the damper 13 is accomplished by the wippen 34 actuated by the key 12 acting through the jack 35 and the damper lever spoon 36. The wippen 34 is an elongated wooden member whose axis lies in a generally horizontal plane. It is pivotally supported near the string end thereof from a downwardly depending wippen flange 37 secured by means of a screw to the lower end of the main action rail 14. The lower extremity of the wippen flange 37 is bifurcated to receive a narrowed bearing portion 38 of the wippen 36. The end of the wippen 36 toward the piano keys, extends downwardly a short distance toward the key. The capstan screw 39, adjustably threaded into the upper surface of the piano key 12, is adapted to transmit motion of the piano key to the wippen 34. A wippen pickup cloth 40 aflixed to the under surface of the wippen is provided at the point of contact between the head of the capstan screw 39 and wippen. As may be noted, when the piano key is depressed, the illustrated 'end bearing the capstan screw 39 is raised, depressing the string end of the wippen 34 and causing'it to rotate in counterclockwise direction as viewed in the drawings about the flange 37.

The jack 35 transmits the above counterclockwise motion of the wippen 34 into upward pressure on the hammer butt 17, and causes impulsion of the hammer 10 against the strings. The jack 35 is an elongated memher having its lower end pivotally supported upon the wippen 34, at a point approximately two thirds of the length of the wippen from the string end of the wippen. A short integrally formed projection 41 on the lower portion of the jack furnishes a recessed seat for the jack spring 42, which tends to bias the upper end of the jack in a counter-clockwise direction as viewed in the drawings--a direction to bias the jack into its lowest or driving position on the hammer butt 17. As illustrated, the helical jack spring 42 is also provided with a cooperating recessed seat in the upper surface of the wippen 34.

In :order to more thoroughly understand the manner in which the jack 35 drives hammer, the construction of the hammer butt must now be considered in somewhat greater detail. The hammer butt 17 is of a B shape, wherein the straightface is oriented toward the strings 11, while the doubly curved portion is oriented toward the keys. The upper curved portion 43, corresponds to and will be designated the hammer butt heel, which engages the back check 44 for purposes to be subsequently explained. The lower curved portion 45 engages the 11pper tip of the jack 35. Both curved portions 43 and 45 are covered with a thin layer of buckskin. Underlying the buckskin on the lower portion 45 there are provided additional cushioning felts at the place where the driving force of jack is exerted upon the butt. At the lowermost extremity of the hammer butt and extending perependicularly therefrom, the hammer butt felt 46 is secured. The hammer butt felt 46 serves to position the upper end of the jack 37 in operating position under the hammer butt against the biasing force of the jack spring 42.

Due to the curvature of the lower butt portion '45, the jack can only exert a solid driving force when it is in position against the hammer butt felt 46. As the upper end of the jack is rotated further away from its driving position, the contact withthebutt becomes more oblique, until, when contact occurs at the upper part of the curve portion 45, no appreciable driving force can be exerted upon the butt by the jack 37. This feature is used to disengage the jack and so control the length of the driving stroke.

The length of the driving path of the jack 35 upon the hammer butt .17 is controlled by the regulating mechanism comprising the jack'spoon 47, the regulating button 48, mounted in the regulating rail 49. The jack spoon 47 is supported in the jack projection:41, and extends at right angles to the axis of the jack 35 towards the keys to a position directly beneath the padded regulating button 48. When the key end of the wippen 34 is elevated when the key is depressed, the jack 35 is elevated also and its upper tip continues to exert an upward force against the hammer butt 17 as the jack is elevated until the jack spoon 47 encounters the stationary regulating button 48. When this occurs, continued upward motion of the wippen 36, causes clockwise rotation as viewed in the drawings of the jack away from the hammer butt driving position, compressing the jack spring 42, and terminating the driving impulse. The point at which driving force is discontinued is controlled by elevation or depression of the regulating button 48 upon the stationary regulating rail 49. In general, disconnection is adjusted to occur when the hammer is approximately on eighth of an inch away from the string.

Retraction of the damper 13 from the string occurs as the hammer is impelled toward the string. At the same time that the key end of the wippen 34 is being elevated to drive the jack against the hammer butt 17, the string end of the wippen 34 is being depressed. Depression of the string end of the wippen causes the damper spoon 36 to be pressed into engagement with the lower extremity of the damper lever 24, thereby rotating the damper 13 as a unit away from the engagement with the string. At the point of engagement of the damper spoon 36 with the damper lever 24, a small damper lever felt 50 is provided. The felt 50 extends up beyond the upper surface of the spoon to pad the damper lever when operated by the pedal actuated damper rod 51, shown nested against the main action rail 14.

The back check 44 arrests the hammer 10 as it recoils from the string to permit timely insertion of the upper tip of the jack 34 in driving position under the hammer butt for the next blow. The back check provides only a momentary halt to the hammer when the keys are quickly released. When the key is not immediately released, the back check locks the hammer in checked position. The locking retains the wippen and all the parts attached to it, as well as the hammer in fixed position until the key is released. In accordance with the invention, and by virtue of other measures now to be described, including the hooked hammer spring 52, the back check 44 also serves as the means to hasten the return of the hammer 10 to its rest position against hammer rail 53. Figure 2 illustrates the piano action in checked position prior to release of the key, and Figure 3 illustrates the piano action immediately after release of the key, having allowed time for the jack to swing into operating position.

The back check 44 is a short wooden member having a felted concave surface 57 adapted to slidably engage the upper curved portion 43 of the hammer butt in checking the-hammer. A small piece of felt 54, secured to the upper surface of the hammer but-t 17, provides a maximum limit to the distance that the hammer can recoil before checking occurs, thus making a positive checking position. The back check 44 is supported from the key end of the wippen 34 upon a stiff back check wire 55. The upper portion of the back check is perforated as shown in 58, and the upper edges are provided with felting 59 to receive the hooked end of the hammer spring 52.

The hooked hammer spring 52, in the embodiment illustrated in Figures 1, 2 and 3, consists of a short helical coil having two axially extending ends. The shorter of these two ends is used to position the hammer spring upon the felt 54 upon the upper surface of the hammer butt 17. For simplicity in assembly, the shorter end may be placed in the hammer shank recess. The longer end of the hammer spring 52 is somewhat longer than the helical portion thereof and is somewhat S shaped, having two regions of opposite curvature as illustrated in the drawings terminating in an upwardly extending hook 56.

The longer portion of the spring is adapted to passlthrough the felted edge 59 of said aperture 58 in operation of the piano action. The helical coil portion of the hammer spring preferably consists of four or five turns, although for convenience in illustrating a smaller number are shown biased to urge the hook portion 56 upward, i. e. in a counterclockwise direction of rotation about the point of support of the spring as viewed in the drawings, and as will appear, to urge the hammer to rest position.

Quick return of the hammer 10 to the hammer rail 53 is facilitated by the hooked hammer spring 52 which engages the back check and so couples the hammer to the faster falling wippen 34. When the hammer, which has just struck the string, is in close proximity thereto. The center of gravity of the hammer lies on the string side of the hammer pivot point, so that gravity is of nov help in returning the hammer to the hammer rail 53 and actually tends to pull it toward the strings. The hammer spring 52 biasing the hammer back away from the strings offsets this pull of gravity, thus preventing blocking of the string and overcoming the initial sluggishness which might otherwise occur during the first portion of the hammer return. The initial return pull on the hammer arises from the reaction from upward pressure of the long portion of the spring 52 against the upper surface of the back check perforation. It should be noted that upon striking the key, the wippen 36 simultaneously elevates the jack 35 and the back check 44 with respect to the hammer butt 17. Elevation of the back check 44 with respect to the butt 17 relaxes in a substantial amount the backward reaction upon the hammer by the spring 52. Figure 2 indicates generally this effect, by showing the long end of the spring 52 extending in a somewhat more perpendicular direction from its seat on the hammer butt, than shown in the rest position. This relaxation is very advantageous in seating the jack under the butt, but must not be sufiicient to prevent a net backward force against the hammer when it is near the string. The spring 52 should always exert sufiicient return bias to offset the forward gravitational pull upon the hammer.

The greatest amount of acceleration on the hammer occurs after checking, when the back check 44 and wippen 34 begin to fall from the position to which they were elevated. As may be appreciated from an inspection of the drawings, the principal weight upon the wippen 34 is concentrated far to the right of its pivot point. This weight includes the jack 35 and the back check 44. Since the weight is falling almost vertically, the back check tends to fall very rapidly under the influence of gravity as soon as the key is released. Accordingly, when the key is struck and released the back check starts to fall. As it falls, the spring 52, engaged by its straight portion, tends somewhat loosely to pull the hammer back. As the back check continues to fall, its lowering position with respect to the hammer butt tends to increase the return bias of the spring upon the hammer, until the book 56 engages the back check orifice. At the moment of engagement of the hook 56 with the back check, the stiffness of the spring increases considerably, causing rapid acceleration of the hammer along with the rapidly falling wippen.

The sequence of events of hammer operation may now be stated in time sequence. As the key 12 is struck, the key end of the wippen 34 is elevated, raising with it the jack 35 and the back check 44. The jack engaging the hammer butt 17, impells the hammer forward until it is approximately one eighth of an inch away from the string. At that instant, the jack spoon 47 engages the regulating button 48, rotating the jack out from driving engagement with the hammer butt. The hammer rebounds backward approximately five eighths of an inch from the string, and slides to a halt against the back check 44. Checking momentarily stops the return motion of the hammer until the key is released. Then as the wippen anemia?" 3'4 is released by thekey and begins to fall, the'jack'35 is slid back into driving position under the biasing force of the spring 42. Prompt seating of the jack 35 is facilitated by the initially relaxed pressure of the hammer spring 52, and the pressure of the jack against the hammer butt 17 which retards the hammer slightly until the jack gets well on its way under the hammer butt.

After the jack has reached driving position against the buttfelt 46, the wippen 34 is still falling, carrying the back check 44 along and exerting an ever increasing backward pull on the'hammer through the spring 52. The accelerating pull increases until the hook on the spring is engaged, and'the hammer is brought smartly to the hammer rail, where it awaits the next blow of the key. The wippen is of sufficient weight to follow any fast repetitive motion given to the keys by the panist even though slightly slowed by the inertia of the hammer. The final stiff engagement of the hammer spring hook with the back check attached to the wippen, accelerates the hammer so thatit obtains full benefit of the force available near the end of the hammer return stroke.

While the hooked hammer return spring 52, illustrated in'Figures l, 2 and 3 has been found to be particularly effective, the spring may take other forms. One such form is shown in side elevation in Figure 4. The spring 52', shown in Figure 4, has a somewhat S-shaped or inflected body portion having two regions of opposite curvature, terminated with a book. The spring 52' may be of circular section or of fiat rectangular section, the latter having somewhat greater durability. The purpose of the infiexion in the body section of the spring is to reduce the initial backard pressure exerted upon the hammer to the minimum required to prevent blocking and still insure lively hammer return, as discussed previously. In some arrangements, the back check may rise sufficiently high so as to make the inflection unnecessary.

Figure 4 illustrates a simplified regulation arrangement. If one employs a deformable material for the spoon 47, the regulating rail 49 need not have an adjustable button as shown in Figures 1, 2 and 3. Instead, for regulating of the piano, a tool may be used to adjust the position of the spoon upon the jack, and thus control the point at which the jack is disconnected from the hammer butt.

The piano actions illustrated in the figures are of simple design adapted to make assembly and disassembly easy.

The upper part of the action including the hammer and damper l3 assemblies are shown assembled on an integral hammer damper flange 22. Since the hammer spring 52 requires no rail between the hammer and damper, and since the damper spring is supported on the flange 22, all these parts may be removed as a unit.

The' assembly and adjustment of the lower part of the action likewise is greatly simplified. By locating the back check 44 and jack between the main action rail 14 and the regulating rail 49 (49), the lower part of the action'is held in place when the keys 12 are removed, since theback check comes to rest against the rail. At the same time, the regulating buttons are made readily available for adjustment by their placement outside the action.

A further simplification achieved by this design is that by locating the jack and back check in close proximity to one another, the portion 43 of the hammer butt heel at which. the back checking occurs, may now be formed integrally with the portion 45 of the butt with which the jack coacts. Close proximity of the jack 35 and back check 44 is further permitted by offsetting a part of the regulating spoon 4-7 to permit passage around the back check wire 55.

Thelength'of the detent'or catch portion 56 is usually set so that there is a small clearance between the catch and the abutting-surface of the back check when the action is in rest-position. When this is true, the moment at which most positive engagement occurs is usually approximately three quarters of the way toward rest position, and the engagement is of a momentary nature. When the hammer is sluggish, the more positive engagement will occur somewhatsooner in the return path of the hammer. When the coiled type of hammer return spring is employed, there is always a slightly resilient action in the coupling between the hammer and the back check. in general, the initially loose backward urging of the hammer spring followed by an increasingly positive backward urging has been found to be most satisfactory. It is of course essential that the initial loose backward urging be adequate to prevent blocking, as in dicated in earlier portions of the specification, and that the ultimate more positive urging provide efiicient coupling of the available return force from the wippen to the hammer.

The detent or hooked end portion 56 of the member 52 may take a number of simple shapes to provide a substantially positive engagement with the back check. While an open hook is shown, passing through a circular hole, other demountable arrangements, such as a closed loop adapted to pass through a narrow slot in the back check when twisted into proper orientation may be used.

From the foregoing it will be readily apparent that an upright piano action constructed in accordance with the present invention has many advantages over the conventional type, and while the invention has been illustrated in preferred forms, it is to be understood that it is not to be limited to the specific constructons in which it is herein illustrated and that it may be practiced in other forms which rightfully fall within the purview. of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An upright piano action comprising a pivotally mounted hammer and an operatively associated wippen and jack, a back check mounted on said wippen, said back check having a block on its upper end, said block having a perforation therein, a spring attached to said hammer adjacent its pivot, said spring engaging in said perforation and being upwardly biased into engagement with the top of said perforation in all positions of said hammer and wippen.

2. The upright piano action set forth in claim 1, wherein the extremity of said spring engaging in said perforation has a detent for substantially positive engagement with said back check. 7

3. An upright piano action comprising a pivotally mounted hammer and an operatively associated wippen and jack, a back check mounted on said wippen, said back check having a block on its upper end, said block having a perforation therein, a spring attached at one end to said hammer and having at the other end thereof a detent for substantially positive engagement with said back check, said spring slidably engaging in said perforation and being upwardly biased into engagement with the top of said perforation in all positions of said hammer and wippen.

4. An upright piano action comprising a pivotally mounted hammer and an operatively associated wippen and jack, a back check mounted on said wippen, said wippen being pivoted to cause elevation of said back check relative to said hammer upon operation of said action, said back check having a block on its upper end, said block having a perforation therein, a spring attached to said hammer adjacent its pivot, said spring slidably engagaing in said perforation and being upwardly biased into engagement with the top of said perforation in all positions of said hammer and wippen, said elevation of said back check providing an initial partial relaxation in upward biasfollowed by a more positive coupling as the point of engagement progresses to the extremity of said spring. 7

5. An upright piano action comprising a pivotally mounted hammer and an operatively associated wippcn and jack, a back check mounted on said wippen, said back check having a block on its upper end, said block having a perforation therein, a spring attached to said hammer adjacent its pivot, said spring slidably engaging in said perforation and being upwardly biased into engagement with the top of said perforation in all positions of said hammer and wippen, the portion of said spring slidably engaging in said perforation being inflected into a S-shaped configuration terminating in a hook providing an initial relaxation in upward bias followed by a more positive coupling as the point of engagement progresses to said hook.

References Cited in the file of this patent 6. The upright piano action set forth in claim 5 wherein 5 216374238 said spring is provided with a central helical portion, aligned with the general axis of said spring.

7. The upright piano action set forth in claim 5 wherein said spring is of flattened rectangular section.

UNITED STATES PATENTS Waite Feb. 8, 1876 Osterberg June 2, 1891 Hastings Aug. 11, 1891 Anton May 31, 1892 Moore Mar. 7, 1893 Osterberg May 30, 1893 Moore Jan. 2, 1894 Perry Apr. 16, 1895 Goble Aug. 31, 1920 Finholrn Feb. 7, 1939 Schultz May 17, 1949 Murdock May 5, 1953 FOREIGN PATENTS Canada Feb. 6, 1951 

